A communication network represented by the Internet provides a best-effort service. That is, when communication traffic passing through a network resource (transmission channel bandwidth) exceeds the sum of bandwidths, the transfer rate is not guaranteed.
Hence, when transferring a file, it is difficult to predict the file transfer time (the time necessary from the start of file transfer from a transfer apparatus of a transmission source to the end of file transfer at a transfer apparatus of a transmission destination).
To solve this problem, a method is used in which a requested transfer completion time is designated in advance for file transfer, and transfer control is performed to complete the file transfer up to the designated requested transfer completion time. This method is disclosed in, for example, reference 1 (Japanese Patent Laid-Open No. 2001-237886), reference 2 (Japanese Patent Laid-Open No. 2000-270010), and reference 3 (Japanese Patent Laid-Open No. 2005-244880).